JPS5853345B2 - Driving method of matrix type liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a driving method for a matrix type liquid crystal character display device, and specifically, to provide a driving method optimal for low voltage time division driving of a liquid crystal character display device.

Conventionally, it has been known to drive a liquid crystal numeric display device using a static driving method. According to this method, for example, in a liquid crystal numeric display device with 7 segments, 1 decimal point, and N digits, the number of external connection terminals is 8N+1 (1 becomes the back electrode of the liquid crystal), and as the number of digits increased, the number of external connection terminals also increased significantly, making the peripheral circuitry for driving more complex, which led to a corresponding decrease in reliability.

Furthermore, when attempting to implement a peripheral circuit into an LSI (Large Scale Integrated Circuit), if the number of external connection terminals is large, one LSI would normally be required, but two LSIs would be required, resulting in a correspondingly more expensive drive circuit.

In addition, since the static drive method requires a large number of external terminals, in order to reduce the number of external connection terminals, for example, as shown in ``Nikkei Electronics J (1972, 5°8), multiple X electrodes and multiple A method has also been proposed in which time-division driving is performed on a matrix-type liquid crystal display device in which characters are displayed by combinations of display points that intersect with Y electrodes, but time-division driving causes problems with crosstalk. .

A method to eliminate crosstalk is the voltage averaging method (the display point is 100% when the display point is selected, and 100% when the display point is half-selected and non-selected).

However, in the conventional voltage averaging method, the switching element of the output stage of the drive circuit is
A breakdown voltage of 0.05 m is required, and this has been a major barrier to converting the drive circuit into an IC or LSI.

The present invention was devised in view of the above points, and its object is to provide a novel driving method capable of low-voltage time-division driving in a matrix type liquid crystal character display device.

The present invention is characterized by a plurality of X electrodes and a plurality of Y electrodes.
In a matrix type liquid crystal display device in which characters are displayed by combinations of display points that are intersections with electrodes, vot vlj V2 and 1 are approximately 0 (however, ■1 is approximately 100 ■) at the X electrode.

, v2 is approximately 100V. ) are selected as appropriate, and one of these two voltages is applied to one of the following two display period units during the display time unit, and the other one voltage is applied to the two display period units. During the display time unit in other periods, vo,
1. ■ Appropriately select two of the voltages of 2 and approximately 0, and use one of these two voltages as the other voltage during the display time unit in one cycle of the two subsequent display cycle units. When given in the display time unit in the other display cycle unit, and viewed in two display cycle units, the display point in the selected state has approximately + ■
o, approximately −■ in other periods.

When a voltage of 1 is applied to a display point in a half-selected state, 1 is approximately +100 ■ in one cycle.

, almost 100 ■ in other cycles. When voltage is applied to display points that are in the non-selected state, there is approximately one point in one cycle.

, in other periods, a voltage of approximately +-■o is applied.

Other objects and features of the present invention will become clear from the description based on the following examples.

FIG. 1 shows a configuration diagram of an embodiment of the present invention. In a matrix type liquid crystal character display device, the intersection of the X electrode 3 and the Y electrode 4 is the display point, and characters are displayed at 4×8 display points. Let's do it.

One character is displayed by a combination of display points that are intersections of a plurality of X electrodes and a plurality of Y electrodes.

These X electrodes 3 and Y electrodes 4 are connected to an X drive circuit 8 and a Y electrode, respectively.
It is connected to the drive circuit 6 and driven.

The four Y drive circuits 6 and the eight X drive circuits 8 are referred to as a Y drive circuit array 5 and an X drive circuit array T, respectively.

The Y drive circuit array 5 includes a scanning circuit 9 consisting of a ring counter.
A scanning signal and a clock having a frequency of 2fR generated from the clock generation circuit 14 are input.

Note that the scanning frequency of the scanning signal is synchronized with the clock of frequency fR generated from the clock generation circuit 13.

On the other hand, an output signal from a character generation circuit 10 consisting of a decoder and a clock from a clock generation circuit 14 are input to the X drive circuit array 7.

The clock from the clock generation circuit 14 is sent to the inverter 15.
The phase of the clock signal is inverted and input to the Y drive circuit array 5, and the phase of the clock of the X drive circuit array 7 and the phase of the Y drive circuit array 5 are reversed.

The output signal of the character generation circuit 10 is synchronized with the clock generated from the clock generation circuit 13, and is synchronized with the scanning of the Y electrode.

Therefore, the input signal that determines the output character of the character generation circuit 10 is given from the memory 1 that stores the characters to be displayed on each Y electrode, and the output signal of the memory 1 is synchronized with the clock generated from the clock generation circuit 13. This is synchronized with the scanning of the Y electrode.

The display character information given to the memory 1 in this manner is converted into a drive signal for the liquid crystal character display device 1, and is applied to the liquid crystal character display device in a time-division manner to turn it on.

At this time, the display characters are rewritten, that is, the memory 1 is rewritten by the display character input device 12, which is connected to an arithmetic circuit in the case of a desktop electronic computer, and to a timekeeping circuit in the case of a watch.

FIG. 2 shows an example of the drive waveform according to the present invention,
Electrode signal Vx, Y electrode signal Vy, display signal Vx -V
y is shown divided into four states.

V in FIG.

is the lighting voltage of the liquid crystal. That is, in a certain display cycle unit (2), the drive is performed in the state shown in (2) in FIG. 2, and in the next display cycle unit (2), it is driven in the state shown in (3), and this process is repeated.

In the period of the display cycle unit I, the X electrode signal continues to be ■ during the display time unit Tw when selected.

, 100"・2'""when not selected・"When electrode signal's selected"
``Ding ■ when choosing between two choices.

becomes. As a result, the signal Vx -Vy applied to the display point is +■o when in the selected state, +IVo when in the half-selected state, and 1-cho when in the non-selected state.

becomes. In the period of the display cycle unit (■), the X electrode signal and the Y electrode signal in the state of the display cycle unit I are exchanged, and the signal Vx-Vy applied to the display point is one (2) in the selected state.

, when in a half-selected state, it becomes 1-Vo, and when in a non-selected state, it becomes +iVo, and the polarity is opposite to the state of ■.

In this way, the AC drive voltage averaging method is realized in terms of two consecutive display cycle units.

If a time-division drive method with a duty ratio of 1/N is adopted using the waveform shown in Figure 2, the selected point (display point to be lit)
The effective value vs1 of the applied voltage is as follows.

Further, the effective value vS2 of the applied voltage at the non-selected point (display point that is not lit) is as follows.

The effective value of the lighting threshold voltage for the square wave signal is vth
Then, in order to prevent crosstalk and turn on the liquid crystal character display device, the following relationship holds true from equations (1) and (2).

Substituting equations (1) and (2) into equation (3), Then, ■Organize about o becomes.

Now when N=4 (when the duty ratio is 1/4), (4
) formula becomes, and when N=8 (when duty ratio is 1/8),
Equation (4) is as follows.

Therefore, when N=4 and vth=6 V, (
Equation 5) is 10.4V≦■o≦18V, and it can be understood that low voltage driving is possible.

The waveforms of the signal applied to the selected point and the signal applied to the non-selected point when N=4 are shown in FIGS. 3A and 3H.

Here, T is the display period unit, and Tw is the display time unit.

A specific drive circuit (first
Examples of drive circuits (corresponding to the drive circuits 6 and 8 in the figure) are shown in FIGS. 4, 5, and 6.

In FIG. 4, Ql, Q2. Q3 is a switching transistor, R, 2R, and 4R are resistors, 22°23.24 is a NOR gate, 21 is an inverter, A is an address, and C is a clock.

Table 1 shows the relationship between the on/off states and output voltages of switching transistors Q1 to Q3 with respect to address A1 and clock C.

As is clear from Table 1, any combination of addresses AJ and Clock C can produce any output voltage.

. A hundred ■.

,0. ■ o is obtained. Table 2 shows the relationship between the on/off states and output voltages of switching transistors Q1 to Q3 with respect to address A and clock C in FIG.

Similarly, those in FIG. 6 are as shown in Table 3.

In FIGS. 5 and 6, R1 and R2 are resistances and D.

D2 is a diode, 31 and 34 are inverters, 3233
is Noah Gate.

The only difference between FIG. 5 and FIG. 6 is that the connection of diode D2 is different, and the other features are the same.

In FIGS. 4 to 6, address A corresponds to the outputs of the scanning circuit 9 and character generation circuit of FIG. 1.

Figure 7 shows the duty ratio ±(N
4) shows the operating waveforms of each part during line sequential scanning.

X electrode signal is Vx, X address is AX1, X electrode clock is Cx, Y electrode signal is V3y, Y address is Ay, Y.
The electrode clock is shown as Cy, and the display point signal is shown as Vx-vy.

The X drive circuit applies a clock signal Cx, and applies a signal of "1" level to the X address when selected, and a signal of "0" level when not selected.

At this time, the X electrode signal becomes Vx.

Similarly, in the Y drive circuit, a clock signal Cy having an opposite phase to Cx is applied, and a signal of "1" level is applied to the Y address when selected, and a signal of "0" level is applied when not selected.

The Y electrode signal at this time becomes Vy.

As a result, the selected state has shi■o, and the half-selected state has ±d■
.

A time-division driving method for a matrix type liquid crystal character display device is realized by the AC driving voltage averaging method.

2 Sho-'1''0 Example''''・Lighting electrical property, t, v,,=
One hundred v.

From these combinations, the display points will be displayed at 2 o in the selected state, and at 100 in the half-selected and non-selected states.

Since we applied a voltage of 1 2
1 2 Ruga 1. v.

The meaning of ,,vo is 1. vo=v2. , v. When = V1 ■.

〉■1〉■2〉0, and the voltage ■.

, ground potential v1. Any combination of voltages v2 may be used as long as the voltage applied to the display point can be applied to the selected state, and the voltage approximately ±TVO can be applied to the half-selected state and the non-selected state.

As described above, according to the present invention, low voltage driving is possible, so that
The breakdown voltage of the switching elements used in the drive circuit is ■.

Furthermore, the X drive circuit and the Y drive circuit have the same circuit configuration, and can be easily integrated into a large-scale integrated circuit in combination with other logic circuits.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIGS. 2 and 3 are diagrams showing an example of drive waveforms according to the present invention, and FIGS. 4 to 6 are diagrams each showing a specific example of a drive circuit according to the present invention. , FIG. 7 is a waveform diagram for explaining the operation of the present invention. 1... Matrix type liquid crystal character display device, 3...
...X electrode, 4...Y electrode, 5...
・Y drive circuit row, 6...Y drive circuit, 7...
...X drive circuit row, 8...X drive circuit, 9.
...Scanning circuit, 10...Character generation circuit,
11...Memory.

Claims (1)

[Claims] 1) In an IJ square type liquid crystal display device, characters are displayed by a combination of display points that are the intersections of a plurality of X electrodes and a plurality of Y electrodes. , v2, and approximately O (however, ■1 is approximately 0.000. ■2 is approximately HVo), and one of these two voltages is applied to one of the following two display cycle units. A voltage of medium voltage in the display time unit in one period is applied to each display time unit in the other period of the two display period units, and also to the Y electrode. , ■1. ■ Appropriately select two of the voltages of 2 and approximately O, and use one of these two voltages as the other voltage during the display time unit in one period of the two subsequent display period units. When given in the display time unit in the other cycle of the display cycle unit and viewed in two display cycle units,
The display point in the selected state has approximately +■ o in one period and approximately 1 ■ in the other period. A voltage of approximately +Vo is applied to display points in a half-selected state, and a voltage of approximately +Vo is applied in one cycle, and approximately -1Vo is applied to display points in a non-selected state in the other cycle. , approximately −■ −V in one period. , in other periods, the voltage of approximately 10±■ is 3
1. A method for driving a liquid crystal display device, characterized in that an application voltage of 300 V is applied.